DE1719457B2 - Device for the recovery of a solvent - Google Patents

Description

The pressure is at atmospheric pressure or kept at spherical pressure, with an inlet for the waste product and outlet for the concentrated waste product and the evaporated solvent. _A pressure pump for feeding the waste product under pressure into the centrifugal thin-film evaporator, a heater for heating of the waste product under pressure above the melting point of the lower and through an adjustable valve for opening the pressurized and heated waste ^{rod into the centrifugal} thin-film evaporator.

The object on which the invention is based is achieved in that the waste product is heated under pressure and in this state is released into a centrifugal thin-film evaporator via a means of " relaxation", the pressure: thin-film evaporator being kept lower, Ij it is the pressure of the waste product is equivalent to.

Further features of the invention emerge from the following description in connection with the Claims and the drawing. It shows

1 shows ^a schematic representation of a device according to the invention, which comprises a heater and a centrifugal thin-film evaporator,

ρ i g. 2 is a schematic representation of another Embodiment of the device, which has a heater, an evaporator and a centrifugal thin-film evaporator having,

Figo shows a further embodiment of the device according to the invention, which consists only of a centrifugal thin film evaporator,

F i g. 4 shows a longitudinal section through the centrifugal thin-film evaporator with a relief valve provided in the inlet,

Fig. 5 is a section along the line VV of

Fig. 6 shows a section through the expansion valve

according to FIG. 5 _{,, ^ n} ■,

F i g. 7 is a schematic representation of a conventional one Apparatus comprising an elongated tube evaporator and a centrifugal thin film evaporator includes.

First, the conventional apparatus for recovering solvent by means of the Fig. 7 will be explained. The device shown in this figure has an elongated tubular evaporator 26, which is a centrifugal thin film evaporator30 upstream of the pre-evaporator of the waste product, so as to reduce the load on the To reduce centrifugal thin film evaporator, which increases the amount of waste product which can be processed by this thin film evaporator. During the operation of the Device becomes the thin liquid waste product from which the solvent can be recovered should, first introduced into an elongated tubular evaporator by a feed pump 25, in which it is vaporized. The resulting mixture of vapors and liquid wedge is in a condensate collector "7, in which the liquid is separated from the vapors. The thickened in this way Waste product is inevitably through the evaporator 26 and by means of a circulation pump 28 the conditional collector 27 circulated. By means of a Pump 29 is withdrawn from the circuit of the higher concentration waste product and a part of the Centrifugal thin-film evaporator 29, introduced, in which the waste product finally thickened will. However, this conventional device has the disadvantages explained at the beginning.

The device for recovering solvent according to the invention will be described with reference to the illustrations. In the embodiment according to FIG. 1, a waste product is introduced into a heater 2 by means of a pressure pump 1 under a pressure of about 8 to 15 kg, cm ^{2 G.} In the heater 2, the waste product is ^{heated to a temperature of about 150 to 200 °} C., for example by steam, without generating steam in the waste product, whereby the enthalpy of the waste product in the liquid state is increased. The waste product is then expanded in a centrifugal thin-film evaporator 4 via an expansion valve 3, as a result of which a substantial part of the solvent evaporates.

With reference to FIGS. 4 and 5, the relaxation process will now be described in more detail. The vapor-liquid mixture, which results from the expansion of the waste product through the expansion valve 3, enters the centrifugal thin-film evaporator 4 via an inlet nozzle A , the vapor being separated from the liquid by a rotor 16 which rotates in this centrifugal thin-film evaporator 4 will. The liquid which did not evaporate due to the relaxation is pressed under the effect of centrifugal force against the inner wall of a drum 15, on which it forms a thin layer. The liquid which forms this thin layer is evaporated by the heat of a heating medium which circulates within a heating jacket 17 which is arranged around the drum 15, whereby the solvent is removed from the liquid. The remaining polymers are discharged through a discharge opening B. The solvent that has evaporated from the relaxation and the heated wall of the drum 15 passes through the space between the rotor 16 and the drum 15 and is discharged through a steam outlet opening C. The heating medium, which circulates within the heating jacket 17, is introduced via an inlet D and leaves the heating jacket via an outlet E.

To avoid recondensation of the solvent vapor, a further heating jacket is provided which surrounds the front end of the drum, a heating medium flowing inside this heating jacket keeping the solvent vapor at the required temperature. The heating medium is introduced into the heating jacket 18 through an inlet F and discharged through an outlet G. Another embodiment of the device according to the invention is shown in FIG. 2 shown. In this embodiment, the waste product is subjected to a pre-concentration under pressure, with it being heated at the same time, in order not only to increase the enthalpy 60, but also to increase the concentration of the waste product to a certain degree before the waste product enters the centrifugal Thin-film evaporator is relaxed into it. The waste product strained into the centrifugal thin film evaporator cnt-65 is processed in the same way as above with reference to FIG. 1 described, treated. In the present case, however, it should be noted that during the heating and the pre-concentration

tration contained in the waste product Polymers must be kept in the dissolved state in order to keep these polymers in the tube evaporator and the condensate collector used for this purpose.

The operation of this device will now be described in detail. The waste product is first introduced into the elongated tubular evaporator 6 by means of a feed pump 5, in which it partially evaporates. The resulting mixture of vapor and liquid is in the condensate collector 7 passed and the vapors separated from the liquid. The thickened and the vapors The freed waste product is forced to circulate by means of a circulating pump 8 through the evaporator 6 and the condensate collector 7 continued to thicken. The vapor pressure in the circuit becomes controlled by a valve 9, so that the pressure does not drop below a certain value. As a result this increases the boiling point of the thickened waste product and increases the enthalpy.

The waste product thickened in this way is partially withdrawn from the cycle and returned to the Centrifugal thin-film evaporator 11 relaxed via an expansion valve 10, the vapors from the liquid are separated and the solvent is completely removed from the liquid at the same time Will get removed.

F i g. 3 shows a further embodiment of FIG Device for the recovery of solvent according to the invention. This device is the Adapted recovery of solvent from a waste product which has already been heated and therefore has a sufficient enthalpy. In this case the waste product is pumped out by means of a pressure pump 12 is fed directly to a centrifugal thin-film evaporator 14 and expanded via an expansion valve 13. Treatment of the waste product inside the centrifugal thin-film evaporator takes place in the same way as with the Apparatus according to FIG. 1. If the heating of the waste product in the preceding process step is carried out under normal pressure and not under excess pressure has been carried out, a solvent recovery effect similar to that described above can be achieved was achieved in that in the centrifugal thin film evaporator 14 negative pressure is generated and the heated waste product is expanded into this negative pressure.

An advantage of the invention is that the method for recovering solvent from waste product carried out continuously with high yield without clogging the device This advantage can be achieved through the use of a centrifugal thin film evaporator can be brought about, in which a rotor is provided, which is made of insoluble polymers existing agglomerates, which form due to the expansion of the waste product, inevitably divided and thereby a clogging of the centrifugal thin-film evaporator with these agglomerates prevented.

In order to obtain this advantage of the invention described above to the full extent, it is necessary to prevent evaporation of the waste product in the heater or in the circulation tubes connected upstream of the centrifugal thin-film evaporator. To this end, an expansion valve is provided at the inlet of the centrifugal thin film manifold, as shown in Figs. 4 and 5 is shown. The precise design of the expansion valve is shown in FIG. 6 shown. In the expansion valve, a valve seat 19 is arranged as close as possible to the outlet 20 so that the waste product introduced into the valve via the inlet 21 cannot evaporate within the valve body 22. In the event that evaporation is made possible within the valve body 22, the waste product is thickened, insoluble polymers precipitating which adhere to the valve body 23 and to the valve rod 24 and thus render the valve ineffective.
The invention will now be further illustrated by means of examples:

example 1

A waste product produced by a polypropylene production facility and containing n-heptane with approximately 3% polymers dissolved therein under different conditions for the recovery of n-heptane in the device according to FIG. 1 treated. The following results were obtained.

attempt temperature Throughput In the poly No. of the tubes Waste product meren ver heater permanent solvent ( ⁰ O (kg / h) (%) 1 70 20.2 3.2 2 167 49.7 2.1 3 · 192 96.7 2.7

The centrifugal thin-film evaporator used, of a horizontally lying conical design, had a heating area of 0.1 m ² . The centrifugal thin-film evaporator was operated at atmospheric pressure, while the tube heater was operated at a pressure of 10 kg / cm ² G. If the waste product in the tube heater is heated more than in experiments 2 and 3, the greater part of the waste product is evaporated due to the expansion in the centrifugal thin-film evaporator, and that part of the waste product which is not evaporated by expansion, quickly increases to the boiling point of the solvent at atmospheric

spherical pressure due to the effectiveness of evaporation cooled by relaxation, the boiling temperature being lower than the precipitation temperature of polymers. However, since the waste product that was not evaporated by the rotor, which is in the Ztntrifugal thin film evaporator rotates, inevitably is broken up, the remaining solvent is evaporated and the polymer temperature is increased, whereby the polymers are discharged in the liquid state through the discharge opening.

In experiment # 1, the waste product was not heated significantly and the recovery of the Solvent results only from the evaporation capacity of the centrifugal thin-film evaporator. In in the cases of experiments 2 and 3, however, the end

thalpie of the waste product has been sufficiently increased by heating in the tube heater before the Waste product was expanded into the centrifugal thin-film evaporator, so that the return

gev is

gel lf Vi Be to ni

d e e e c

recovery rate in these cases is several times higher than in experiment 1.

Example 2

A waste product derived from a polypropylene production plant containing isobutyl alcohol with 1.5% polymer dissolved therein was used in the device according to FIG. 2 among different Conditions treated to recover isobutyl alcohol. In this case the device became according to FIG. 2 used to thicken the waste product to some extent before it is put into the Centrifugal thin film evaporator was relaxed, with the preconcentration of the waste product was carried out under pressure with simultaneous heating. This is because of the latent heat of vaporization of the solvent is so great that heating of the waste product in the tube heater in the same way as in Example 1, only an increase in pressure and not an increase the amount of solvent, which would result in the expansion in the centrifugal thin film evaporator should be evaporated, whereby a sufficiently high yield can accordingly be expected. The results were the following:

attempt
No.

Throughput

temperature
in the
Pre-concentration

(kg / h) ( ⁰ C)

Concentration of
Waste product after
the preconcentric
tion

(Weight percent)

In the
Polymers
remaining solvent

10.3
110.0
189.0

160
160

less than 3 less than 3 less than 3

When trying Ni. 1, the waste product was relaxed directly into the centrifugal thin-film evaporator, which was designed as a horizontally lying, conical evaporator with a heating surface of, lm ² , without it had previously been heated or evaporated in the tube heater.

It can be seen from the results that the

Yield of solvent in a treatment according to the invention is several times higher than in

if> the case in which the centrifugal thin-film evaporator is used alone.

Example 3

From a polyethylene production plant became a waste product, which hexane with 0.6% in it dissolved polymers in the same manner as in Example 1 using the device according to FIG. 1 treated to recover hexane. The results are shown below:

Attempt throughput
No.

(kg / h)

Outlet temperature at
Tube heater
( ⁰ C)

Remaining in the polymers
solvent

25.3

62.7

115.0

20th
150
180

2.6
2.5
2.8

In experiment No. 1, the waste product was expanded into the centrifugal thin-film evaporator without being previously heated in the tubular heater, while in experiments 2 and 3 the waste product was heated under pressure before it was expanded in the centrifugal thin-film evaporator. From the above results it is clear that the yield is höhei of solvent in the latter several times in the first ils.

For this purpose 2 sheets of drawings

509541 /:

Claims (1)

17 19 457 i In the production of polypropylene was previously _n . often a steam-powered evaporator for back patent claim: extraction of solvent from the waste product ^ "J ^ t γϊ3 ρς, however, around an intermittent one Device used for the recovery of a solution. Ua it sic j. by means of a waste product that is from a 5 Betneb, bnngi. oie β γ Propylene plant or for the production of polyethylene poly ^ P ^ J ^ f ^^ SS ^ Λ fdas homologous polymers derived that the WaraievemBi se g _{of Entfernune} and in which the boiling point of the solvent * seit.gung the ^Polvm ^ '^ M ^ S ^{tntlernun of} at Wsphärendruck is lower than the Schmel, - ^ u ^^ VJE ^ dead ^ "r ^ ^ ^ point of the polymer, marked under so lcne π uui,, _f - ■■. . by a centrifugal thin-film evaporator Zentnfugal-Dunnsch.chtverJan ^ fers tur de konn- (4,11,14); which is kept at a nuable recovery of solution under atmospheric pressure, n the lying pressure or at atmospheric pressure ^^. ^^^^^ t ^ S ^^, ^^ , with an inlet for the waste- Ing.Techn Bd 26, 1954 p 574) the £>"™" g "J-Jrodukt and outlets for the concentrated _iS Dünnsch.chtverdampfer-is particularly effective as a waste product and the evaporated solvent waste product by eines.Rotors, Jr, a DruckDumpe ( I ₄ S, 12) Turn supply of the waste product inside this evaporator turns against the wall by pressure in the centrifugal of the evaporator and in the form of a thin-film evaporator, a heater (2,6) to treat the thin layer -Heating of the waste product under pressure via the so dung of a Zentnfuga 1-Dunn.ch.ch evaporator, _t melting point of the polymer and by means of a valve (3, 10, 13) that can be adjusted to recover the solution mixture (3, 10, 13) to relax the the polymer-containing waste product fat un Pressurized and heated waste to be carried out completely. However, the amount of «J» waste product in the centrifugal thin film product is usually so large that the dampers get into it. * 5 sole use of the Zentnfugal-Dunnsch.cht- Evaporator for the treatment of the waste product, the system costs grow extremely high leaves. It is therefore to reduce the investment costs essential to increase the amount of waste product. 30 which a single centrifugal thin film evaporator can process. For this purpose the The invention relates to a device for reconcentrating the waste product before it is fed in a solvent from a waste solution in the centrifugal thin-film evaporator product that contains the solvent to be recovered. Circulation of the waste product over a long and contains polymers, namely, polypropylene, poly-expanded tube evaporator, and a condensate ethylene and homologous polymers. collector increased. Such a procedure is inadequate In the production of z. B. Polypropylene is a waste product only up to such a point Solvents are used in large quantities, and can be concentrated to the extent that it is the Auirccnt waste product, which is derived from the production plant preservation of the circulation through the pipe evaporator is, contains atactic polymers that 40 fer allowed. Furthermore, it is disadvantageous that the in as a by-product through the polymerization reaction, the waste product is present and insoluble were, as well as low molecular weight polymers, the substances containing polymers to the were generated by incomplete polymerization. Walls of the elongated tubular evaporator wah-Zur Recovering the solvent from the end of the thickening accumulate and that unios waste product these polymers must be separated in the polymers containing substances will. Condensate collector in which a separation of Although some of these polymers takes place in the solvent vapor and liquid, agglomerate and are dissolved, the greater proportion of the polymers lies in a clogging of the condensate collector Solvents in solid form, which call each other. The one from UIlbeim also has these disadvantages Let the waste product stand. This 50 man's encyclopedia. Vol. 1, 1928, p. 29 and from the Polymers tend to agglomerate in a document published by the German Palentdampfer and clog the pipes in this registration G 16 363 IVa / 53e known prior art damper as well as the lines, the technology connected to it, in which the waste product in the are. Evaporator is relaxed. One way of recovering the solution is to develop a device by means of a polymer-containing waste for the recovery of solvent / u 'proHuk' is to use a conventional one which avoids the above disadvantages and has to use a vaporizer. However, the use of a high efficiency with low installation costs conventional evaporators with can be operated continuously, which consist in the fact that the polymers, which contain insoluble substances, even with a small device for recovering the solvent Concentrations of the waste product on the pipe- dissolved from the waste product, accumulate Jas from a plant walls and prevent the continuous operation- for the production of polyethylene, polypropylene or wise the evaporator. In addition, homologous polymers are derived and in which the viscosity of the waste product during the 6 ₅ boiling point of the solvent at atmospheric pressure removal of the solvent is very high, which is lower than the melting point of the polymer, the degree of solvent recovery is essentially characterized by this device is decreased. Centrifugal thin-film evaporator that focuses on: